The present invention relates generally to apparatus and methods for spinal abnormalities.
The prior art includes many different apparatus and methods for treating spinal conditions. Known apparatus may utilize elongate plate members having several aligned collinear openings for screws fixed in vertebrae which frequently are not collinear. To match the collinear screw openings with non-collinear fixed screws, the physician must attempt to contour the plate in the frontal plane. See FIGS. A and B which illustrate the traditional rod or plate system.
Alternatively, the screws may be bent to accommodate the plate openings. Both alternatives may be intraoperatively impossible or impractical.
Placement in a less than optimum position or trajectory in the pedicle to provide alignment with the plate openings may require undesirable pedicle cutout or fracture and nerve root injury.
Other known apparatus for treating spinal deformities are disclosed in U.S. Patent Nos. 5,104,412 and 5,181,917. These apparatus comprise elongate rod members combined with vertebra engaging means. The rods are essentially straight with the consequent need for specially formed connectors.
Accordingly, there is a need in the art for a method and apparatus for treating spinal conditions which avoids the problems of the prior art, permits attachment to nonlinear points on adjacent vertebrae, and provides increased bone volume for grafts or fusion.
The present invention provides an apparatus and method or system for treating spinal conditions by moving a vertebra to a desired position with respect to additional vertebrae or maintaining the vertebra in the desired position.
The apparatus of the present invention may include a plurality of link members that can be secured to adjacent vertebrae in chain-like fashion utilizing pedicle bolts or screws that are not collinear with each other. Use of the link members permits subdivision of multiple nonlinear pedicle fixation points into two point units interconnectable with a single link member.
The present invention thus facilitates multiple point fixation, schematically shown by FIG. B, using two points at a time to overcome the problem in the prior art of nonalignment between plate openings and pedicle screws. The links, once secured to the pedicle screw or bolt with a locking nut, form a chain. The result is a construct securely affixed to the vertebrae.
The link members are in the form of plates or rods with opposite end portions and a central portion. The links may be generally flat precontoured, for example, to correct lordosis or kyphosis or to impart torsion. Alternatively, the flat links may be contoured by surgeon incident an operative procedure. The opposite end portions each have an aperture therein configured to receive attachment means affixed to the pedicle of adjacent vertebrae. The central portion for each link member is preferably offset from the end portions to expose substantial portions of adjacent vertebrae to which the link member may be attached. The invention also includes links in which the central portion is not offset.
This offset provides increased vertebrae bone volume, useful bone grafts and fusion as compared with prior art apparatus which overlie the vertebra surface. In addition, the present invention permits visualization of bony maturation using plain X-rays since the links do not overlie the graft area.
The links may be used with pedicle screws, bolts, or pedicle or laminar hooks. A combination of hooks and screws or bolts can be used as well depending on the particular application of the invention. For example, a laminar hook can be used on a lamina that is being fused to avoid damaging its associated facet (joint) such as would be caused by a screw or bolt.
The surface of the link member of the present invention is preferably provided with radial cuts or other means adjacent the apertures in the end portions for enhancing the locking engagement of the links with a pedicle bolt, screw, hook, another link or other spinal implant members. The bolt or hook has a threaded extension portion that cooperates with a locking nut, and a wedge-shaped washer if needed, to secure an end of the link member to a vertebra.
The wedge-shaped washer compensates for a lack of parallelism in the axial plane between adjacent bolts or screws.
An additional aspect of the present invention is that link members may be used to secure contralateral chains (formed as described above) to each other at their ends, and/or points intermediate their ends, to form a quadrilateral or ladder-shaped construct having increased torsional stability.
It is frequently difficult to make a tight connection between a non-aligned series of implanted bone bolts. For example, in a spinal construct, bone bolts are rarely aligned for connection of a plate or rod. The adjacent bone screws are usually independently located with respect to each other in three dimensional space, which creates an offset distance of some kind between the bolt and the plate/rod connection. See FIG. A. The offset problem has been addressed by providing connectors that accommodate the non-linearity of the adjacent bolts implanted in a series. There is a limit to the adjustability of the currently available connectors when S used with traditional bone bolts and bone screws.
An important object of the invention is to provide polydirectional bone bolts or screws with effective pedicle purchase which may rotate up to 360xc2x0 for sagittal plane variability. Sagittal plane adjustment is achieved through the rotation of the polydirectional screw head reducing the need for significant contouring of the associated links. See generally FIGS. A and B (comparing traditional rod and plate system with the link and polydirectional screw system of this invention).
A multi-angle bone bolt is also needed for use in any bone fixation system in which uneven bone portions are to be connected to a bolt whereas angulation of upper and lower portions of the bolt will provide a more effective and secure bone fixation system.
FIGS. 9A, 9B, 9C, 9D, 10A and 10B of application Ser. No. 08/692,821, now U.S. Pat. No. 5,716,357 which is a continuation of Ser. No. 08/448,566 (PCT/US94/11463) illustrate spinal fixation devices including one form of a multi-angle or multi-directional screw.
The invention permits manipulation of the spine before the link is placed with consequently more accurate, quantifiable adjustments and improved visualization. The link design allows medialized placement in the lumbar spine and lateralized placement in the thoracic spine. Greater surgeon accessibility to the bone graft site optimizes the graft bed and the useful volume of bone graft.